I still keep thinking I want to do something from a book I once read.
Basically aliens with 2016 tech invade Earth in 1943.

You mean the Race from Harry Turtledove's WORLD WAR series?

I have a soft spot for that book series; even if it is kind of drecky, because it was one of my first introductions to a comprehensive epic book series.

I've actually thought about designing a mod to do this; and it would have to be a mod set in 1944-45 using the WinSPMBT engine to allow for the various weapons the Race uses; and using bits and pieces of late WW2 kit floating around in the Post WW2 OOBs.